The invention relates to systems equipped with batteries, in particular systems equipped with batteries formed by battery modules arranged in series, and in particular automobile vehicles with electric or hybrid drive.
In general, in these systems an electric converter is used for supplying a load with power from the direct current, which can be supplied by a battery. In particular used are converters such as inverters for supplying an electric motor with sinusoidal currents, three-phase currents for example. The converter and the motor form a powertrain.
The batteries can be composed of a plurality of battery modules arranged in series, and the modules can be independently placed in series or not, i.e. switched. In other words, according to the voltage desired to be supplied to the load, a greater or lesser number of battery modules is activated. The voltage at the terminals of a battery can therefore vary during the operation of a system.
Conventionally, a capacitor is placed between the battery and the load so as to smooth the high-frequency currents as well as the inrush currents absorbed by the converter. When the battery (i.e. the assembly of modules) is connected to the converter by means of relays, for example within a vehicle during startup, strong inrush currents occur and may damage the components, for example the capacitor, the relays used or even the power switches. Additionally, when the voltage at the terminals of the battery varies, currents can occur, as the battery and the capacitor both behave as voltage generators.
Furthermore, jerks generated by the motor can occur when the voltage varies at the terminals of the battery.
Consequently, the capacitor is generally charged so that the voltage at the terminals of this capacitor is equal to the voltage at the terminals of the battery after it has varied.
European patent application EP 2 361 799 may be referred to, which describes a system for increasing the voltage at the terminals of the capacitor before connecting the powertrain, i.e. a pre-charge system for the capacitor. This document in particular proposes the use of a resistor for forming an RC-type circuit for charging the capacitor. A drawback of this system is that it does not allow the capacitor to be charged completely, the duration of charging being too long. Another drawback of this system is the addition of a resistor in series to the system. This system can therefore only be used on startup of the vehicle on account of this resistor. It is therefore not suited to the activation or the deactivation of a battery module during the operation of the vehicle.
American patent application U.S. 2012/0025768 may also be referred to, which describes a system for pre-charging a capacitor comprising a resistor of low value, and an assembly of switches for improving the pre-charging of the capacitor. This system is also not usable during the operation of the vehicle.
International patent application WO 2009/077668 describes a pre-charge system for a capacitor in which a switch is connected in series with the capacitor, and this switch is controlled by a pulse-width modulation signal, the duty cycle of which varies. A drawback of this solution is that it increases the impedance of the branch comprising the capacitor.
Lastly, French patent application FR 2 923 962 may be referred to, which describes a system for pre-charging a capacitor using a boost-type power converter, but which also has the drawback that it increases the impedance of the branch comprising the capacitor. It is hence impossible to use this system during the operation of the vehicle on account of overly large losses caused by the increase in the impedance.